A partial dentary of an adult tyrannosaur from the Dinosaur Park Formation of Alberta, Canada, preserves the embedded tooth of another tyrannosaur within the bone. The specimen’s incompleteness precludes generic identification of either the jaw or the embedded tooth, although Gorgosaurus and/or Daspletosaurus are most likely given the stratigraphic position. The absence of healing around the lesion indicates the bite took place either post-mortem or within weeks prior to the death of this animal. A post-mortem bite can be explained by confamilial or cannibalistic scavenging. Alternatively, the bite would represent a perimortem instance of intrafamilial aggression that may have resulted in the death of that animal. An estimated 6053N of bite force was required to produce the bite mark. This specimen provides the best evidence for aggressive peri- or post-mortem confamilial interaction among tyrannosaurs and corroborates previous studies based on inferred tooth marks. □Alberta, behaviour, Campanian, Cretaceous, Dinosaur Park Formation, Theropoda, Tyrannosauridae.